Skin Diseases That Cause Dark Spots. 1  Melasma: Itâs one of the commonest causes of grayish patches on the face. It mostly affects the forehead, cheeks, or the area between your mouth and nose. 2  Riehlâs Melanosis: It causes grayish or brownish patches on your face resulting from hyper-pigmentation.
In biology, tissue is a cellular organizational level intermediate between cells and a complete organ.A tissue is an ensemble of similar cells from the same origin that together carry out a specific function. Organs are then formed by the functional grouping together of multiple tissues.The study of tissue is known as histology or, in connection with disease, histopathology.unctions of epithelial tissue: 1  the cells of the body surface form the outer layer of skin. 2  inside the body, epithelial cells form the lining of the mouth & alimentary canal & protect these organs. 3  epithelial tissues help in absorption of water & nutrients.
Princeton's WordNet (0.00 / 0 votes) Rate this definition: tissue (noun). part of an organism consisting of an aggregate of cells having a similar structure and function. tissue, tissue paper (verb). a soft thin (usually translucent) paper. weave, tissue (verb).